My wife needs the HHR tomorrow, so I'm just adding more Dex-cool (50/50 mix) today (in the rain), and testing temperatures before tearing stuff down (if needed). So far, I've added 3/4 gallon to the radiator (none to overflow container, and will burp the system tonight & tomorrow am), and took the HHR on the same road test. The t-stat opens at 180 degrees, the fans come on at 217 degrees (they always have), but the A/C clutch never engages. It can't be the sensor, because the DIC always reads the temperatures. What else should I order to get all running anew (along with new cap, t-stat, all new Dex-cool), after I've repaired her car and truck, first. The HHR will work as-is for the immediate week ahead. I still can't believe I didn't look at the coolant before now.

 

Cracked ac condensator ? No pressure in ac system. Clutch won't engage

 

I've been busy working on the wife's vehicles, so I've gotten away from the HHR problem. GMC starter replaced; Cobalt's brake system drums adjusted, front rotors & pads are new, bled the brakes and replaced old fluid...but still not fixed...new master cylinder ordered... I've been busy. Hurt my back again, too.

No apparent damage to A/C system, still has freon. Tried jumper-ing the A/C clutch relay (pin 87 to 30 on the relay), with no success (could've missed the connection due to too thick a jumper not fitting into slots). I'll try again with proper gauge wires.

I've been thinking (a bad sign): could the ECT sensor (which always sends good info to the DIC/temp gauge) have sent a high temperature to the ECM (or BCM) to tell it to cut-off power to the A/C clutch when the engine temperature rose to 240+, while the radiator was 1 gallon low (now fixed). The ECM/BCM might have the "shut-down" message still in memory, and that's why there's no signal allowing the clutch to work?

As I said, no codes were set (I cleared the system with my scan tool anyway), no fuses or relays bad, and the radiator fans do come on automatically at 217 degrees (but not when the A/C control button is pressed and lit). Should I disconnect the power from the BCM/ECM (not sure which), to erase a possible shut-down message from memory?

 

I'm leaning toward the freon pressure switch. There is a diode in the under hood fuse box that may be a suspect.

No, the BCM is not an AI, just a simple collection of transistors.

 

After driving the Panel off-on over the past four months, with the refilled coolant keeping the car at the proper temp automatically (T-stat opening OK, fan starts if 217 degrees is reached, avg coolant temp 181 while driving). I or the wife have driven it every week, once or twice, in those four months, long highway and multi-stop shopping trips included, with zero problems. Didn't replace T-stat or sensor.

I never looked further again, into the A/C problem until today, finally seeing if the system had freon (it does), then using a paper clip to jumper the clutch into operation (while putting in more freon), and getting A/C outlet temperature down to 38F (ambient is 80F). Withdrawing the paper clip, I tried switching around several Omron 21997403 relays, but none would activate the clutch. Is it the control box on the dash, or the infamous "freon pressure switch" on the compressor that's bad? Hate to spend the $$$ to get one or the other, and having to put it into a shop for the latter.

Got all the parts (Master Cylinder), tools (Metric set, line wrenches, power bleeder, bench bleeding kit), bi-directional scanner (Foxwell NT510, to auto-bleed the ABS) needed to fix the Cobalt, but the battery now is dead, so that's another $125-150. Yesterday, the electric clothes dryer burnt out (master control unit and heating coil on a 21 year-old Admiral...not worth trying to fix), so I spent $700+ on a new one. It seems like everything is going out at the same time (P.S. the wife had me put in two ceiling fans yesterday, also), so there's that expense. So, once again, the HHR may sit on the back-burner (still usable on cooler days, not 90-110F), as long as the wife's '98 GMC runs, and so does my '04 2500HD Chevy (I replaced the GMC's A/C control last year, the blower resistor, too), and the freon is topped up on both so they have 38-40 degree air.

Thinking about remote jumping the compressor relay from inside while driving (did it on my old '86 S-10, for 15 years). But, I'd rather fix it right, though.

 

Use your paper clip to jumper the pressure switch? There is a diode in the fuse box that would be easy to check.

 

I jumpered terminals in the base of #15 A/C clutch relay (30 power to 87 output) to get it to engage; previously I swapped diodes 9 A/C clutch with 58 windshield wiper, with the wipers still getting power, so assumed that both diodes were OK. I didn't try the paper clip in the pressure switch, yet. Which terminals bypass it?

 

I posted the wires for you to figure it out. The way to test a diode is the check for continuity in both directions, good diode conducts in one direction only.

At RockAuto the switch ranges from $15-$34.

 

Diodes are OK, pulled ECM fuse for 10 minutes: no change, the clutch still remains a problem. You must be right, the pressure switch may be bad. Though I never got the P0128 code, it must've triggered the fault, anyway. I'll have to read up on the pressure switch...I'm no good at wiring lately (really not ever), so I don't want to short out the sensor or ECM by crossing wires. I may just try my new bi-directional scanner (bought to fix the Cobalt's ABS/ autobleed the system, to see if it can show me what is wrong.

 

Pressure switch has nothing to do with P0128, that is the t-stat and t-sensor.
It would be the black/wht and gray wires. If anything broke it would be the variable resistor. The org/black should have an output between 0V and 5V. All of that is in the diagram, if you know what to look for. The squiggly line with an arrow represents a variable resistor moderating voltage being fed by Low ref (digital 0 volts/analog ground) and 5v ref (exactly 5 volts).